Optical networks have become a standard technology for the transport of information in the telecommunications industry. A number of different optical network standards have been defined, with each having advantages and disadvantages for different uses. Synchronous optical network (SONET) is one standard for optical telecommunications transport. SONET is expected to provide the transport infrastructure for worldwide telecommunications for at least the next two or three decades. The increased configuration flexibility and bandwidth availability of SONET provides significant advantages over the older telecommunications system, such as reduction in equipment requirements, increase in network reliability, ability to carry signals in a variety of formats, a set of generic standards that enable products from different vendors to be connected, and a flexible architecture capable of accommodating future applications, with a variety of transmission rates. SONET is often used for long-haul, metro level, and access transport applications. In metropolitan areas, the access network often includes high-capacity synchronous optical network (SONET) rings, optical T3 lines, and copper-based T1s.
The management (control, monitoring, and provisioning) of a given SONET network is typically done via operator initiated command messages on a designated controlling host computer system directly connected to one of the network elements (NE's) in the SONET network. Command messages targeted for NE's, other than the directly connected NE, are transported over the optical connections between the NE's using a small portion of the optical bandwidth of the data transport overhead referred to as the Data Control Channel (DCC). Typically, NE's are optically connected to more than one NE in the SONET network requiring an NE to employ routing tables to direct messages on a DCC path leading to the NE for which it is targeted. SONET networks most generally employ OSI routing protocol also over the DCC's between NE's to dynamically populate the routing tables for each NE in the SONET network.
For SONET networks that employ OSI protocol (or any routing protocol scheme, such as OSPF), wherein each NE maintains a routing table entry for every NE in the network) there is generally a limit on the number of directly addressable NE's (for example 255 NE's). This limit is enforced to prevent the DCC's between NE becoming overburdened with OSI protocol messages used to exchange routing information between NE's). Such a limit assures that most of the DCC bandwidth between NE's is used to carry command messages.
Conventionally, one way to reduce the OSI routing burden in a SONET network is to split the network into more than one addressing area. For example, a single SONET network may be split into two separate address areas. Then, to interconnect the networks, one network element in the newly configured network becomes a member of both addressing areas. In this configuration, all control messages from one network area destined for the other network area must pass through the network element sharing membership with both network areas. For this reason, splitting the network into two separate addressing areas often results in a crippling burden on the network element sharing membership in both network areas due to extra control message traffic between the two areas.
Accordingly, there is a need for a technique for addressing additional network elements within a single SONET network. There is a further need for a technique to configure a SONET network to have a large number of network elements in a single addressing area that does not suffer from an excessive OSI routing burden.